Pumping apparatus



y 1966 R. G. TROUT 3,250,440

PUMPING APPARATUS Filed Dec. 23, 1963 3 Sheets-Sheet l INVENTOR ROBERTG. TROUT May 10, 1966 R. G. TROUT 3,250,440

PUMPING APPARATUS Filed Dec. 23, 1963 3 Sheets-Sheet z INVENTQR ROBERTG. TROUT A'ITORNEY May 10, 1966 R. G. TROUT PUMPING APPARATUS 3Sheets-Sheet 3 Filed Dec. 23, 1965 mm. ww. 3. QW- \3 mm. NM m w //H i mmr WI. E, N a a "M we mw. m m NN. ----Q M ow. E g V m qmf [J MA hm. mm mll.. WWI/l All .3 F 2 Nm United States Patent 3,250,440 PUMPINGAPPARATUS Robert G. Trout, Altadena, Calih, assignor to FMC(Zorporation, San Jose, Calif., a corporation of Delaware Filed Dec. 23,1963, Ser. No. 332,386 9 Claims. (Cl. 222255) The present inventionpertains to a pumping apparatus and more particularly to an apparatusfor pumping substantially all of the liquid from a reservoir, withoutthe formation of air vortexes which would cause the apparatus to becomeair-bound, and while maintaining the vol ume of liquid being pumped perunit of time at a predetermined amount.

The problem solved by the apparatus of the present invention exists inthe removal of liquid from a reservoir and, more specifically, liquidcargo from the hold of a tanker. As is well known, the ships hull formsthe bottom of the hold in order to maximize the amount of liquid thatcan be transported. Small external sumps are not used since they wouldextend below the bottom of the vessel and thereby the subject to damageas well as to increase the drag on the ship. Small internal sumps arenot built into the ship since they would result in the loss ofconsiderable space which could otherwise be used to carry cargo.

Conventionally, a high capacity multi-st-age centrifugal pump is loweredinto the hold, positioned with its inlet adjacent to the bottom, andoperated to pump the liquid therefrom. Although capable of removing mostof the liquid with no difiiculty, previously known pumps of this typehave been unable to remove the last twelve or so inches while operatingat the same high pumping rate. The reason for this inability is that asthe liquid level nears the bottom of the hold, air vortexes form in theliquid around the inlet to the pump. These vortexes, and there may beseveral of them around the pump inlet, may be visualized as whirlingfunnels of air which have a maximum diameter at the surface of theliquid and converge downward to a tip at the pump inlet'. As a result,air is drawn into the pump with the liquid. This causes the pump toair-bind, that is to fill with so much air that its liquid dischargeessentially disappears.

In order to remove most all of this last foot or so of liquid, otherprocedures must be resorted to. First, the operator usually reduces therate of flow through the pump; this has the effect of eliminatingvortexes at least until about six more inches are pumped out. At thislevel, a high volume pump is ordinarily unable to remove any moreliquid. And yet, these six inches of liquid must be removed since theymay represent dozens of barrels of a saleable commodity.

Thus, it has been known to use complicated air separating systems on thecentrifugal pump, to pressurize the hold, or to use a low capacity, highhead pump, in an effort to strip the hold of these last several inchesof liquid. These auxiliary methods and apparatus for stripping the holdare more time consuming and more expensive than regular high capacityoperation of the centrifugal pump. Extra labor is required to installthe dilferent pumps and apparatus for carrying out these auxiliarymethods. The ship is at dockside longer, resulting in higher costs andaggravating congestion at the port.

This background of the problem brings the present invention into sharpfocus, for a high capacity pumping apparatus embodying one form of thepresent invention can remove all of the liquid from a hold, with theexception of about one barrel, while operating at full capacity; and ifit embodies another form it can remove essentially all of the remainingliquid.

It is an object of the present invention to provide an improved pumpingapparatus.

3,259,446 Patented May 10, 1966 Another object is to provide anapparatus for pumping substantially all of the liquid from a reservoir,without the formation of air vortexes which would cause the apparatus tobecome air-bound, and while operating the apparatus at a predeterminedhigh rate of flow.

Another object is to provide a pumping apparatus which minimizes thetime, expense, and labor involved in pumping liquid out of a reservoir,such as the hold of a tanker.

Another object is to achieve high volume pumping while removing theliquid in a reservoir to a minimum distance from the bottom thereof.

Another object is to control the maximum velocity of liquid flowingthrough a circumferential passage into the inlet of a pumping apparatuswhich passage is defined between the bottom of a reservoir containingthe liquid and the apparatus.

These, together with other objects, will become apparout upon referenceto the following description and accompanying drawings in which:

FIG. 1 is a fragmentary diagrammatic transverse section of a tanker andshows a pumping apparatus including a vortex hood embodying the presentinvention mounted on the tanker and projecting into the hold thereof.

FIG. 2 is an enlarged side elevation of a portion of the pumpingapparatus with portions being broken away and in section and showsspecific details of a frusto-conical form of the vortex hood in closelyspaced relation to the bottom of the hold.

FIG. 3 is a transverse section taken on a plane at a position indicatedby line 3-3 of FIG. 2.

FIG. 4 is a plan view of a frusto-pyramidal form of the vortex hood foruse in certain installations instead of the hood of FIG. 2.

FIG. 5 is a diagram contrasting the results achieved with the subjectapparatus and with conventional apparatus.

FIG. 6 is a view similar to FIG. 2 but shows another form of the pumpingapparatus.

Referring more particularly to the drawings, a portion of a tanker 10 isschematically shown in FIG. 1 and is provided with a hold or reservoir12 having a bottom 14 and being capable of containing a cargo of liquid,a small amount of which is indicated at 15 in FIG. 1. The tanker has abulkhead 16, constituting one wall of the hold, and a deck 18.

A pumping apparatus embodying the present invention is generallyindicated by the numeral in FIG. 1. The illustrated pumping apparatusincludes a high volume, high head, multistage centrifugal pump 26 havinga rotary power source 27, such as a steam turbine or electric motor, atubular housing 28 terminating in a lower suetion piece 29, and a vortexhood 30 connected to the suction piece. The present invention isprimarily concerned with this vortex hood and particularly itsrelationship to the bottom 14 of the hold 12 or other reservoir.

The housing 28 of the pump 26 includes a discharge casting projectingdownward from the power source 27 and having an outlet 36 and ahorizontal deck flange 37. The pump is supported on the deck 18 of thetanker 10 by a riser 39 that rests on the deck, receives the housing,and bears the weight of the pump since the deck flange rests on theriser.

The housing 28 also includes a column pipe connected to the dischargecasting 35 and projecting through the riser 39 and downward throughthehold 12. A bowl assembly 46, also constituting part of the housing asdefined herein, is connected to the pipe and projects toward the bottom14 of the hold. Guides, such as 48, encircle the pipe and are attachedto the bulkhead 16.

The pump 26 also has a drive shaft (FIG. 2) connected to the rotarypower source 27 and extending downward through the housing 28. Impellers52 are secured to the drive shaft within the bowl assembly 46, in a wellknown manner. It is thus evident that the tubular housing provides aliquid duct(s) 55 having a lower inlet 56 at the lowermost impeller andan upper outlet 36.

The suction piece 29 (FIG. 2) is frustum-shaped and includes an upperneck 60 bolted to the bowl assembly 46 in circumscribing relation to theinlet 56, an imperforate intermediate wall 61, having an inner convexsurface and an outer concave surface, diverging outward and downwardfrom the neck, and an outer up-turned rim 62 provided with an externalannular groove 63. An O-ring 64 is fitted in this groove forestablishing a primary seal with the vortex hood 36, as will be subsequently evident.

Vertical ribs 66 are secured to the outer surface of the suction piece29 in circumferentially spaced relation therearound, and each rib has anaperture 67 located adjacent to the rim 62. A spider 69 is secured tothe inner surface of the wall 61 and mounts a bearing 70 which rotatablyjournals the lower end portion of the drive shaft 50.

The vortex hood 30 can have various shapes. A frustoconical vortex hoodis identified by the numberal 30a in FIG. 2. This'hood has an upperinner neck 75 encircling the rim 62 of the suction piece 29 and being inreleasably slidable, fluid-tight relation therewith by virtue of theO-ring 64. The hood 30a also has an imperforate intermediate Wall 76diverging downward and outward from the neck 75, and a lower outercircular edge 77 having a predetermined circumference c, to besubsequently described in more detail, and being closely spaced at adistance s from the bottom 14 of the hold 12. For reinforcement, ribs 79are secured externally to the neck, wall and lower edge of the hood.

When the pumping apparatus 25 is used for removing liquid 15 from thehold 12 of a tanker 10, the hood 30a is preferably permanently securedto the bottom 14 of the hold. For this purpose, blocks 78 are welded tothe underside of the lower, outer edge 77 and to the bottom incircumferentially spaced relation to eachother. The outer edge of thehood and the bottom of the hold define an annular flow passage 80 havingan area about equal to the product of the space s and the circumferencec, it being noted that the circumference of the flow passage is actuallyslightly less than the circumference of the outer edge because of theblocks; however, in order to simplify the discussion herein, referencewill be made only to the circumference c of the outer edge since the twoare nearly the same.

With the vortex hood 30a secured to the bottom 14 of the hold 12, thepump 26 can be inserted into the upper neck 75, thereby being coupled tothe hood in fluidtight relation, or can be withdrawn from the hood inorder to be removed from the hold. In the coupled position of the pump,an annular pocket 81'is defined between the neck of the hood and theouter surface of the suction piece 29. As the liquid level in the holddrops below the neck, a quantity of liquid 82, hereinafter referred toas the sealing liquid, is captured in this pocket and constitutes asecondary seal in overlying relation to the primary seal established bythe O-ring 64. Although the O-ring, in itself, is capable of providing asufiicient seal between the suction piece and the hood, insertion andremoval of the pump may damage the primary seal 64 so that the secondaryseal insures fiuid tight coupling. The apertures 67 allow the sealingliquid 82 to flow through the ribs 66, and the upper neck 75 of the hoodhas overflow holes 84 which control the level of the sealing liquid. Inthis manner, a substantially uniform depth of sealing liquid ismaintained in the pocket, circumferentially of the rim 62, in accordancewith the secondary sealing effect required.

It is also to be noted that the vortex hood 30 can be permanentlyattached to the pump 26 without affecting the operation of the pumpingapparatus 25 according to the present invention. However, because of itsrelatively large circumferences c, as will be subsequently more evident,and because it is not required for proper operation of the pump wherestripping a reservoir is not desired, the hood is preferably notpermanently attached to the pump.

Another shape of the hood 30 is illustrated in FIG. 4. Here is shown afrusto-pyramidal hood 39b which is useful for certain installationswhere the available area cannot accommodate a circular hood 36a havingthe desired circumference c. The hood 30b has an upper neck 75b, anintermediate imperforate wall 76b including panel portions 86, and arectangular lower-outer edge 77b having a circumference c. For thereasons described above, blocks 88 are secured to the outer edge 77b forspacing the outer edge at a distance s from the bottom 14 of the hold 12and, if desired, permanently attaching the hood 30b to the bottom.

The selection of the dimensions s and e is of primary importance to thesuccessful practice of the present invention in retarding vortexformation and resultant entry of air into the pump inlet 56. Naturally,the dimension s should be as small as possible since, for practicalpurposes, when the liquid level falls below the edge 77, or 7717, airwill be drawn into the inlet whether or not any vortexes have formed.However, other factors, such as unevenness of the bottom, may requirethe dimension s to be more than the optimum amount.

Once dimension s is determined, it is possible to calculate thecircumference c from the equation Q=kcsv, where Q=the rated capacity ofthe pump 26 k the pump constant v velocity of flow through the passage Ahigh capacity pump, such as the multi-stage centrifugal pump 26, havinga pressure head capable of lifting liquid from the bottom of the hold tothe outlet 36, is selected so that Q and k are known.

As for the velocity v, it was discovered during development of thepre'sent'invention that the velocity of flow through the passage 80should not be greater than about one foot per second if detrimentalvortex formation to prevent air binding of the pump to be retarded untilthe liquid reaches a minimum level. With Q, k, s and v known, 0 isreadily obtained by solving the above equation. Once Q and s areselected, therefore, the opti mum value of 0 actually depends on theimportant velocity factor.

It is obviously not practical to state herein all of the variouscombinations of pump capacities and dimensions s and c that willeffectively strip the hold 12 or other reservoir of liquid. One exampleof the subject apparatus 25, together with the foregoing information onhow to determine the important parameters, will suffice to show othersskilled in the art how to practice the present invention underconditions which differ from those of the example. Thus, assume that thepumping apparatus 25 is to be used for removing kerosene from the hold12 of the tanker 10, and that because of space limitations, it isnecessary to use the frusto-pyramidal hood 30b instead of thefrusto-conical hood 30a. The bottom 14 of the hold is surveyed and otherfactors considered in arriving at a distance s of about /2 inch. Inorder to obtain the desired lift, a nine-stage, turbine drivencentrifugal pump 26 having a volumetric capacity of 500 gallons perminute and operating at 1760 r.p.m. is employed. With the pump capacityQ and the distance s determined, the circumference c is readilycalculated, as above explained. Accordingly, the length and width of theouter edge 77b used in this installation is respectively five feet andtwo feet; it is also to be noted that with these dimensions, thedistance between the bottom 14 and the neck 75b is approximately two andone-half inches.

The hood 3% is, of course, attached to the bottom 14 of the hold 12 whenthe latter is empty, but assuming that the hood is in place and thatliquid is in the hold, the pump 26 is installed. The pump is operated atits rated capacity of 500 gallons per minute and pumping continues atthis rate until air vortexing occurs. With the present invention,vortexing doesnt occur until the liquid level is about where it is shownin FIG. 1, that is, between the neck 75b and lower edge 77b of the hood30b, this usually being two or three inches off the bottom 14. At thislow level, less than one barrel of liquid may be all that remains in thehold. These results are in contrast to those achieved by conventionalpumping equipment where air vortexing and resulting binding of the pumphas usually occurred when there are still dozens of barrels of liquidremaining in the hold.

FIG. 5 is a diagram which contrasts the results obtained by conventionalequipment (on the left) and results obtained by use of the presentapparatus (on the right). The conventional apparatus includes a pumpwhich may be identical with the pump 26 but for purposes of separateidentification herein is given the numeral 95. A conventional suctionpiece 96 is attached to the lower end of this pump and usually has amaximum diameter D about the same as the diameter of the bowl assemblyof the pump. The minimum spacing of the suction piece from the bottom 14is usually A to /2 of D. Under these circumstances, air vortexes 97 andresultant airbinding of the pump occur when the liquid is about at theneck of the suction piece 96; this may be thirteen to fourteen inc-hesoff the bottom, just to give an example for comparison purposes. Inorder to remove any more of the liquid with the pump 95, it is necessaryto reduce its pumping capacity whereupon the liquid level may be reducedto that indicated by the dashed line 98 just above the lower end of thesuction piece. Any further removal of liquid must be accomplished byother apparatus or methods, as suggested in the introduction to thespecification.

By way of contrast, the subject pumping apparatus is showndiagrammatically in FIG. 5 on the same scale as the conventionalapparatus 95. The pump 26 can be operated at its full capacity until theliquid level is below the neck 75, or 75b, of the hood 30, at which timeair vortexes 99 may form. It will be evident, therefore, that thesubject pumping apparatus removes more liquid in less time than aconventional pumping apparatus, it being noted that the same pump isused in each apparatus.

Another form of pumping apparatus embodying the present invention isillustrated in FIG. 6. Since the pump employed in the form of FIG. 6 isthe same as the pump of FIGS. l-S, with one exception, the samereference numerals are applied to corresponding parts with primesuflixes added. The one exception is that the shaft 50' has an endportion 51 extending out of the inlet 56.

Asuction piece 105 has an upper neck 106 bolted to the bowl assembly46', an intermediate wall 107 diverging downward from the neck, and alower outer rim 108 provided with an external groove 109 in which isplaced an O-ring 110. Ribs 112 are secured externally to the suctionpiece, each rib having an aperture 114 therein. As described so far, thesuction piece 105 is identical with the suction piece 29.

This form of the pumping apparatus 25 includes a main vortex hood 120which is identical with the vortex hood 30a and so is described only bybriefly identifying its neck 121, its intermediate wall 122, and itslower outer edge 123 which is fixedly held in predetermined spacerelation to the bottom 14 by blocks 124.

The significant, distinguishing feature of this form of the apparatus isan auxiliary pump 130 of low capacity although having as high a pressurehead as the pump 26. An example of a pump that is suitable for thispurpose is a regenerative turbine vane pump. The form of auxiliary pumpdisclosed has only one stage and operates at a capacity as low as ten totwenty gallons per minute, although having a very high head as stated.The auxiliary pump includes a concave-convex mounting shroud 131rotatably receiving the end portion 51 of the shaft 50' and rigidlysecured to the suction piece by circumferentially spaced webs 132. Ahearing 133 is mounted within the shroud in surrounding relation to theshaft. The pump includes a casing 135 bolted to ribs 136 depending fromthe shroud. The casing has a chamber 138 which is provided with aradially disposed inlet 139, on the left of the shaft as seen in FIG. 6,and a radially disposed outlet, not shown, which is circumferentiallydisplaced from the in let. An impeller 142 is positioned within thechamber and issecured to the shaft. The casing has a lower orifice 144in alignment with the shaft for balancing pressures above and below theimpeller and for draining liquid from the chamber. Such a pump, per se,is known and not described in any greater detail.

The auxiliary pump 130 (FIG. 6) also includes a discharge elbow 150,preferably cast integrally with the suction piece 105 and the mountingshroud 131, having a lower end 151 connected to the outlet of thechamber 138 and an upper socket. 152 above the suction piece. Anauxiliary discharge tube 154 has a lower end threaded into the socket,projects upward alongside of the pump 26, and has an upper outlet, notshown.

An auxiliary vortex hood 160 has a neck 161 bolted to the shroud 131, anintermediate downwardly diverging wall 162, and a lower outer edge 163maintained in spaced relation to the bottom 14 by blocks 165 that aresecured to the auxiliary hood. It is to be noted that the auxiliary hoodis fastened to the auxiliary pump 130 and not to the bottom, in contrastto the main hood 120.

The lower edge 163 of the auxiliary hood 160 is prefcrably spaced evencloser to the bottom 14 of the hold 12 than the outer edge 123 of themain hood and defines a flow passage 166 with the bottom. It is, ofcourse, obvious that the circumference of the lower edge 163 is lessthan the circumference of the lower edge 123.

In operation of the form of pumping apparatus illus trated in FIG. 6,the main pump 26' is operated at its full capacity in order to removeliquid from the hold 12 until the liquid level drops below the neck 121of the main hood 120 where air vortexing occurs, as described above.Since the auxiliary impeller 142 is on the main pump shaft 50', thisauxiliary impeller rotates along 'with the main impellers 5.2. However,the auxiliary pump does not take effect until the main pump entraps somuch air that it ceases to discharge. Thereafter, the main pumpcontinues to work, but liquid is actually being pumped out of the holdby the auxiliary pump and through the discharge tube 154.

Since the capacity of the auxiliary pump 130 is only fractional relativeto the capacity to the main pump 26', the velocity of flow through thepassage 166 is less than one foot per second even though thecircumference of the edge 163 is considerably less than thecircumference c. The advantage of the auxiliary pump is that no shutdownof the pumping apparatus 25' is required to evacuate the hold ofsubstantially all liquid, even though the rate of removing the last twoor three inches of liquid by the auxiliary pump is slower than removinga corresponding amount of liquid by the high capacity main pump. Inconsidering the operation of the auxiliary pump, it is to be noted thatatmospheric pressure forces liquid up into the auxiliary vortex hood andmounting shroud 131 to the inlet 139 as long as no air is admitted underthe edge 163 of the auxiliary hood.

Although the subject pumping apparatus has been described with thesuction piece 29, or 105, connected directly to the bowl assembly 46, or46, it is to be understood that the bowl assembly could be locatedremotely from the suction piece, and that the latter could be directlyconnected to the column pipe 45. It is also to be understood thatalthough the subject apparatus is particularly suited for use with themulti-stage, high capacity centrifugal pump described, the principles ofthe invention are applicable to other types of pumps.

From the foregoing, it will be evident that a pumping apparatusaccording to the present invention is capable of pumping substantiallyall of the liquid from a reservoir, without the formation of airvortexes which would cause the apparatus to become air-bound, and whilemaintaining the volume of liquid being pumped per unit of time at apredetermined amount. As applied to stripping the hold of a tanker, thesubject apparatus is advantageous in withdrawing the maximum amount ofliquid cargo in a minimum of time and with a minimum of expense andlabor.

Although preferred embodiments of the present invention have been shownand described, it will be understood that various changes andmodifications may be made in the details thereof without departing fromthe spirit and scope of the appended claims.

Having described the invention, what is claimed as new and desired to besecured by Letters Patent is as follows:

1. A pumping apparatus comprising a main pump having an inlet, outerwall means circumscribing said inlet and diverging therefrom to an outeredge, and an auxiliary pump mounted within said wall means in spacedrelation to said inlet of the main pump, said auxiliary pump having anauxiliary inlet and inner wall means circumscribing said auxiliary inletand diverging to an inner edge spaced circumferentially inward from saidouter edge.

2. The pumping apparatus of claim 1 wherein a plurality of spaced websrigidly interconnect said outer wall means and said auxiliary pump.

3. The pumping apparatus of claim 1 wherein a discharge pipe isconnected to the outlet of said auxiliary pump and extends through saidouter wall means.

4. The pumping apparatus of claim 1 wherein said main pump is amultistage high capacity centrifugal pump and wherein said auxiliarypump is a single-stage low capacity regenerative turbine vane pump.

5. The pumping apparatus of claim 1 wherein said inv ner edge is in aplane displaced axially endward of the outer edge.

6. The pumping apparatus of claim 1 including a reservoir having abottom, means securing said outer wall means to said bottom with theouter edge spaced from the bottom, and wherein said inner edge is spacedfrom said bottom.

7. A pumping apparatus comprising a high capacity, high head main pumphaving an elongated housing terminating in an endwardly opening inlet, ashaft journalled in said housing and having an end portion projectingout of said inlet, means for drawing liquid into said housing throughsaid inlet, and other frustum-shaped wall means in circumscribingsealing engagement with said housing and diverging therefrom to an outeredge; and a low capacity, high head auxiliary pump having a pump casingmounted on said outer wall means around the end portion of the shaft andin endwardly spaced relation to the inlet of the main pump, said casinghaving a pump chamber positioned so that a plane passing through thechamber is substantially normal to the shaft, said chamber having aradially opening inlet and a radially opening outlet, an impellersecured to the end portion of the shaft and positioned in said chamber,inner frustum-shaped wall means connected to the casing incircumscribing relation to the inlet of the auxiliary pump and divergingdownward to an inner edge spaced inward from the outer edge of the outerwall means, and a discharge pipe connected to the outlet of theauxiliary pump and extending through both'of said wall means.

8. In an apparatus for pumping liquid from a liquid reservoir having asuction piece providing an inlet submerged in the liquid, the inletbeing circumscribed by a peripheral edge that is spacedfrom the bottomof the reservoir, anr whereupon, during entry of liquid into the inletduring pumping, one or more air vortexes form in the liquid and convergefrom the surface thereof to said edge when said surface is at apredetermined level above said edge whereby it is ordinarily necessaryto reduce the volume of liquid being pumped per unit of time below therated capacity of the pumping apparatus in order to eliminate saidvortex formation, the improvement of means for eliminating said vortexesat said predetermined level and retarding the formation thereof untilthe liquid surface is below said level comprising an imperforate hoodhaving an upstanding neck surrounding said inlet in spaced relationtherewith and projecting down and out from said peripheral edge to alower outer edge spaced closer to said bottom than said peripheral edgeand defining a flow passage with said bottom, said flow passage havingan area that is large enough to substantially reduce the flow velocitywith respect to the flow velocity in said inlet so as to allow liquid tobe pumped therethrough at said rated capacity while preventing airvortexes from forming until said surface is below said level, saidsuction piece and said hood being releasably slidably coupled in fluidtight relation, said suction piece and said neck forming an annularpocket therebetween, and liquid in said pocket to establish a secondaryseal between said neck and said suction piece.

9. The means of claim 8 wherein said neck has an overflow passagecommunicating with said pocket.

References Cited by the Examiner UNITED STATES PATENTS 1,943,603 1/1934Hartman.

2,533,697 12/1950 Stewart 222-464 X 3,151,565 10/1964 Albertson et al.222-385 X FOREIGN PATENTS 1,020,237 11/1957 Germany.

RAPHAEL M. LUPO, Primary Examiner. HADD S. LANE, LOUIS J. DEMBO,Examiners.

1. A PUMPING APPARATUS COMPRISING A MAIN PUMP HAVING AN INLET, OUTERWALL MEANS CIRCUMSCRIBING SAID INLET AND DIVERVING THEREFROM TO AN OUTEREDGE, AND AN AUXILIARY PUMP MOUNTED WITHIN SAID WALL MEANS IN SPACEDRELATION TO SAID INLET OF THE MAIN PUMP, SAID AUXILIARY PUMP HAVING ANAUXILIARY INLET AND INNER WALL MEANS CIRCUMSCRIBING SAID AUXILIARY INLETAND DIVERGING TO AN INNER EDGE SPACED CIRCUMFERENTIALLY INWARD FROM SAIDOUTER EDGE.